Ikuko Shibasaki

The effect of glycosylation on plasma N-terminal proBNP-76 levels in patients with heart or renal failure

Objective Pro-brain natriuretic peptide (proBNP)-108 and N-terminal proBNP-76 (NT-BNP) contain seven sites for O-linked oligosaccharide attachment. Currently, levels of glycosylated NT-BNP are probably underestimated because it is not recognised by one antibody in the sandwich assay system. The pathophysiological significance of cardiac and plasma levels of non-glycosylated (nonglyNT-BNP) and glycosylated NT-BNP (glyNT-BNP) in heart failure (HF) and chronic renal failure (CRF) was investigated. Methods Plasma samples from 186 patients with HF and 76 patients with CRF on haemodialysis were studied, together with 11 atrial tissue samples. To measure nonglyNT-BNP and glyNT-BNP, samples were incubated with or without deglycosylating enzymes and NT-BNP was measured using Roche Elecsys proBNP I. The percentage glyNT-BNP was calculated as glyNT-BNP/(glyNT-BNP + nonglyNT-BNP). Results In HF, plasma BNP, nonglyNT-BNP and glyNT-BNP levels all increased with increasing disease severity (New York Heart Association class; p<0.0001), though the molar ratio remained constant (molar ratio, BNP:nonglyNT-BNP:glyNT-BNP = 1:2.4:9.6). Before haemodialysis for CRF, plasma BNP and nonglyNT-BNP were somewhat elevated, and glyNT-BNP was markedly increased (molar ratio, BNP:nonglyNT-BNP:glyNT-BNP = 1:8.5:82). After haemodialysis, plasma BNP, nonglyNT-BNP, atrial natriuretic protein and cGMP all declined (p<0.0001), but glyNT-BNP was unchanged. Notably, the percentage of glyNT-BNP was elevated before haemodialysis, and was further increased after haemodialysis (p<0.0001). Atrial tissue levels of BNP, nonglyNT-BNP and glyNT-BNP were similar. Conclusion The findings suggest that most endogenous plasma NT-BNP is glycosylated and therefore undetectable with the current assay system, and that the relative glycosylation level is increased by haemodialysis.

Association of serum concentrations of irisin and the adipokines adiponectin and leptin with epicardial fat in cardiovascular surgery patients

Epicardial fat located adjacent to the heart and coronary arteries is associated with increased cardiovascular risk. Irisin is a myokine produced by skeletal muscle after physical exercise, and originally described as a molecule able to promote the browning of white adipose tissue and energy expenditure. In order to decrease cardiovascular risk, it has been proposed as a promising therapeutic target in obesity and type 2 diabetes. We investigated the relationships between serum concentrations of irisin and the adipokines adiponectin and leptin and body fat including epicardial fat in patients undergoing cardiovascular surgery. We obtained serum samples from 93 patients undergoing cardiovascular surgery (age 69.6 (SD 12.8) years, BMI 24.1 ± 4.8 kg/m2). Computed tomography (CT) and echocardiographic data were obtained from the routine preoperative examination. Subcutaneous fat area (SFA, cm2) and visceral fat area (VFA, cm2) near the umbilicus were automatically measured using the standard fat attenuation range. Epicardial fat area (EFA, cm2) was measured at the position where the heart became a long axis image with respect to the apex of the heart in the coronal section image. Total body fat mass, body fat percentage, and skeletal muscle volume (SMV) were estimated using bioelectrical impedance analysis (BIA). Serum irisin concentration was measured by enzyme-linked immunosorbent assay, and compared with adiponectin and leptin concentrations. The data were also compared with the clinical biochemical data. EFA was strongly correlated with BMI (P = 0.0001), non-HDL-C (P = 0.029), TG (P = 0.004), body fat mass (P = 0.0001), and body fat percentage (P = 0.0001). Serum leptin concentration showed a significant positive correlation with BMI (P = 0.0001) and TG (P = 0.001). Adiponectin, but not irisin, showed a significant negative correlation with BMI (P = 0.006) and TG (P = 0.001). Serum leptin level had a significant positive correlation with EFA, VFA, and SFA. In contrast, the serum adiponectin level was significantly negatively correlated with EFA, VFA, and SFA. The serum irisin level was also negatively correlated with EFA (r = -0.249, P = 0.015), and SFA (r = -0.223, P = 0.039), and tended to correlate with VFA (r = -0.198, P = 0.067). The serum level of adiponectin was negatively correlated with that of leptin (r = -0.296, P = 0.012), but there were no significant correlations between irisin and either adiponectin or leptin. Multivariate linear regression demonstrated that EFA showed a positive association with serum leptin level (β = 0.438, P = 0.0001) and a negative correlation with serum irisin level (β = -0.204, P = 0.038) and serum adiponectin level (β = -0.260, P = 0.015) after adjusting for age, sex, and BMI. The present study provided the first evidence of associations of the serum irisin and adipokines (adiponectin and leptin) concentrations with epicardial fat in cardiovascular surgery patients. Irisin may play a role in preventing excess adiposity including epicardial fat, and consequently cardiovascular risk in patients.